Characterization of intermediate Cr-C layer fabricated by electrodeposition in hexavalent and trivalent chromium baths

The effect of formic acid and current density on the crystal structure, surface morphology and crystallization of intermediate Cr-C layers deposited in both hexavalent and trivalent chromium baths were studied to observe chrome-carbide formation behavior and to develop an environmental protective Cr-C electroplating technology. Formic acid in hexavalent and trivalent chromium baths effectively produces intermediate Cr-C layers. The intermediate Cr-C layers has initially amorphous type microstructure. Crystallization of the intermediate Cr-C layer occurs at a current density above 27.5 A/dm(2) in a trivalent chromium bath and above 100 A/dm(2) in an hexavalent chromium bath, respectively. The carbon content of the intermediate Cr-C layer prepared in hexavalent chromium bath is twice as much as that of the layer prepared in trivalent chromium bath. Cr23C6 and Cr7C3 were observed in the intermediate Cr-C layer prepared in hexavalent chromium bath, whereas, Cr23C6 was formed in the layer prepared in trivalent chromium bath after vacuum annealing at 800 degreesC. (C) 2003 Elsevier B.V. All rights reserved.